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EP0720001B1 - Méthode pour déterminer la position d'une fibre optique - Google Patents

Méthode pour déterminer la position d'une fibre optique Download PDF

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Publication number
EP0720001B1
EP0720001B1 EP95119165A EP95119165A EP0720001B1 EP 0720001 B1 EP0720001 B1 EP 0720001B1 EP 95119165 A EP95119165 A EP 95119165A EP 95119165 A EP95119165 A EP 95119165A EP 0720001 B1 EP0720001 B1 EP 0720001B1
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EP
European Patent Office
Prior art keywords
filament
light
spatial frequency
spatial
distance
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EP95119165A
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German (de)
English (en)
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EP0720001A2 (fr
EP0720001A3 (fr
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Thomas Joseph Atwood
David Andrew Pastel
Bruce Warren Reding
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Corning Inc
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Corning Inc
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/004—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring coordinates of points
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques

Definitions

  • This invention relates to methods and apparatus for monitoring the position of an optical waveguide fiber or other transparent filament. More generally, the invention relates to methods and apparatus for measuring the distance to an object or to a portion of the surface of an object.
  • US-A-5,066,120 which describes a device for testing an optical system, in particular an ophthalmic lens, in which light which has passed through the optical system is passed through a Ronchi ruling before it reaches a detector.
  • the present invention provides a further capability to fiber monitoring systems of the type described above, namely, the ability to monitor and thus control the position of the fiber as it is being drawn. Such positional information is needed to keep the fiber centered and to monitor tension in the fiber through the measurement of the temporal frequency of standing waves along the length of the fiber.
  • an object of the present invention to provide improved methods and apparatus for monitoring (measuring) the distance to an object, such as an optical waveguide fiber. Further, it is a particular object of an aspect of the invention to provide a position monitor which can be combined with a diameter-defect-coating monitor of the type described above with a minimum addition of hardware.
  • the invention provides a method for monitoring the location of a filament comprising the steps of:
  • the above method can be used to control the location of a filament by adding the further step of generating a control signal for the location of the filament from the value of ⁇ D .
  • the invention further provides an apparatus for measuring the distance to a surface in combination with an object having the said surface, the apparatus comprising:
  • the means for determining the spatial frequency ⁇ D of the spatially modulated scattered light at the detecting means can take various forms. For example, this means can perform fringe counting based on peaks, valleys, and/or zero crossings, with the fringe counting being performed directly on the spatial data produced by the detecting means or on spatial data that has been numerically smoothed or filtered.
  • the spatial frequency ⁇ D is the number of fringes counted divided by the characteristic dimension of the detecting means, e.g., the length of the detecting means.
  • the spatial frequency ⁇ D is determined in the spatial frequency domain by performing a transform, preferably a Fourier transform, of the spatial data produced by the detecting means. Other spatial frequency domain approaches can also be used, if desired, such as a wavelet approach.
  • the system includes a lens system between the spatial modulating means and the detecting means, which has a positive optical power.
  • the distance between the spatial modulating means and the surface becomes a linear function of ⁇ D .
  • the distance measured is that to an optical waveguide fiber and the measurement is used as part of a control system for controlling the drawing of the fiber from a preform.
  • the control system preferably also controls fiber diameter and hermetic coating thickness, and monitors the fiber for defects.
  • Figure 1 is a schematic diagram illustrating the basic elements of a Watkins-type system for measuring fiber diameters using far-field interference patterns.
  • Figure 2 is a schematic diagram illustrating the components of a fiber monitoring and control system with which the present invention can be used.
  • Figure 3 shows a frequency spectrum of a calculated far-field interference pattern of a 125 micron, coreless fiber containing a 5 micron on-center hole.
  • Figure 4 is a schematic diagram of apparatus for practicing the present invention.
  • Figure 5 is a schematic diagram illustrating the effects of locating a detector 31 in the back focal plane of a lens system 27.
  • Figure 6 is a schematic diagram illustrating the geometric relationships used in determining the relationship between ⁇ M at Ronchi ruling 50 and ⁇ D at detector 31.
  • Figures 7 and 8 are stylized drawings of spatial frequency spectra for a defect-free optical waveguide fiber whose position and diameter are monitored using the apparatus of Figure 4.
  • the position of the fiber is the same in both figures;
  • ⁇ M is about 4.0 cycles/mm in Figure 7 and about 12.3 cycles/mm in Figure 8.
  • Figure 9 is a block diagram showing a preferred procedure for generating a spatial frequency spectrum for use in the practice of the present invention.
  • Figure 10 illustrates the linearity of a preferred embodiment of the present invention.
  • Figure 11 illustrates the precision of a preferred embodiment of the present invention.
  • Figure 12 illustrates the use of the invention to determine the distance "D" to a diffusely reflecting surface 113.
  • Figure 4 shows the components of a fiber location monitoring system constructed in accordance with the present invention.
  • Fiber 13 is shown at two locations marked A and B in Figure 4.
  • Light from the fiber passes through spatial modulating means 50, lens system 27, and is detected by detector 31.
  • Detector 31 can be of the type described in the above-referenced U.S. Patent No. 5,309,221.
  • Spatial modulating means 50 has a spatial frequency ⁇ M and spatially modulates the light passing through it at that spatial frequency.
  • the spatial modulating means can be a mask or similar device having a periodic variation in transmission, phase, or other optical property.
  • a preferred form of spatial modulating means 50 is a Ronchi ruling. The following discussion is thus in terms of such a ruling, it being understood that other spatial modulating means can be used if desired.
  • a Ronchi ruling consists of alternating opaque and transparent slits, which can be formed, for example, by placing chrome strips on a glass plate. All of the opaque slits have the same width and all of the transparent slits have the same width, but the widths of the opaque and transparent slits do not have to be the same. Accordingly, in addition to its spatial frequency ⁇ M (given by one over the spacing between, for example, transparent slits), a Ronchi ruling is also characterized by its duty cycle, i.e., the ratio of the width of an opaque slit to the sum of the width of an opaque slit and the width of a transparent slit.
  • a preferred duty cycle for a Ronchi ruling for use in the practice of the present invention is about 0.15, i.e., about 15% of the area of the Ronchi ruling is opaque. This duty cycle is preferred because it provides a relatively high level of illumination at detector 31, i.e., it avoids light starvation problems at the detector. Other duty cycles can, of course, be used in the practice of the invention if desired.
  • Ronchi rulings can be readily added to a diameter-defect-coating monitor of the type shown in Figure 2 by simply mounting a ruling on the fiber side of each of lens systems 26 and 27. Ronchi rulings are commercially available at reasonable cost.
  • Lens system 27 is an optional component of the system which, as explained below, linearizes the output of the distance monitoring system.
  • Lens systems of the type discussed in the above-referenced U.S. Patent No. 5,309,221 can be used in the practice of the present invention.
  • Lens system 27 has a positive optical power, is preferably located between the Ronchi ruling and the detector, and is spaced from the detector by the lens system's focal length "f". That is, the detector is in the lens systems' focal plane, in particular, in its back focal plane.
  • the focal plane of a lens system has the important property that parallel rays in object space intersect the focal plane at a common radial distance from the system's optical axis.
  • Ray 61 originates at the lens system's front focal point 63. Accordingly, after refraction by the lens system, this ray travels parallel to the optical axis as shown at 64 in Figure 5.
  • Equation 1 and Figure 5 can be interpreted as showing that a detector of a given length in the back focal plane of a positive lens system will see the same angular spread of light coming from a fiber, irrespective of the distance of the fiber from the detector.
  • This effect is illustrated schematically in Figure 4 for a detector whose length corresponds to an angular spread of 16° about the optical axis of the lens system.
  • detector 31 sees light in the ⁇ 8° range irrespective of whether fiber 13 is at position A or at position B.
  • FIG. 6 The operation of the distance measuring system of the invention is shown schematically in Figure 6, where 50 is a Ronchi ruling having opaque slits 55 and transparent slits 56 oriented perpendicular to the plane of the figure.
  • the transparent slits 56 are separated from one another by the distance "d” which is equal to 1/ ⁇ M .
  • the Ronchi ruling is separated from detector 31 by the distance "S”.
  • D S ⁇ D /( ⁇ M - ⁇ D ) thus showing that D is a function of ⁇ D and thus can be monitored (measured) by determining ⁇ D for light from the fiber which reaches detector 31 after having been spatially modulated by Ronchi ruling 50.
  • this measurement of D is not dependent, at least to first order, upon the transverse location of the fiber.
  • this can be seen by imagining that ruling 50 is moved upward in Figure 6 by a distance "d".
  • rays 68 and 69 will still strike detector 31 at L 1 and L 2 , respectively, and the above analysis will be unchanged.
  • system performance will begin to degrade as the number of illuminated areas on detector 31 decreases. Eventually, the system will stop functioning as the fiber moves completely out of the system's field of view.
  • Figure 7 shows a spatial spectrum for a system of the type shown in Figure 4 for a fiber having a diameter of about 125 microns, a Ronchi ruling having an ⁇ M value of about 4.0 cycles/mm, and a Ronchi ruling-to-fiber distance "D" which is approximately equal to the focal length "f" of lens system 27.
  • the spectrum includes an O.D. component whose spatial frequency ⁇ OD is about 3.1 cycles/degree and a position component whose spatial frequency ⁇ D is about 4.3 cycles/degree.
  • the spectrum also contains two other components labelled 70 and 71 in Figure 7. These components are the result of heterodyning between the position component and the O.D. component, and appear at spatial frequencies corresponding to the sum and difference of the spatial frequencies of the position and O.D. components, i.e., at about 7.4 cycles/degree (4.3 + 3.1) and about 1.2 cycles/degree (4.3 - 3.1) in Figure 7.
  • a Ronchi ruling having a spatial frequency of 12.3 cycles/mm is preferred for expected Ronchi ruling-to-fiber distances which are approximately equal to the focal length of lens system 27 and for fibers having expected diameters of less than about 200 microns.
  • the heterodynes for such a ruling and, in particular, the lower frequency heterodyne are well above the O.D. component.
  • the position component can disappear (drop out) at certain positions of the fiber.
  • dropouts arise from diffractive effects as the widths of the transparent and opaque slits of the Ronchi ruling are decreased as the spatial frequency increases. It is also believed that the use of a low duty cycle aggravates this problem.
  • ⁇ M 12.3 cycles/mm
  • ⁇ M 12.3 cycles/mm
  • Values of ⁇ M other than 12.3 cycles/mm can, of course, be used in the practice of the invention.
  • the particular value of ⁇ M to be used for any specific distance monitoring system can be readily determined by persons skilled in the art from the disclosure herein.
  • FIG. 7 and 8 The spatial frequency spectra of Figures 7 and 8 can be computed using discrete sequence Fourier transforms as disclosed in the above-referenced U.S. Patent No. 5,309,221, and that approach is preferred when high precision is required.
  • the procedure will be discussed in terms of a detector which has 2048 pixels, it being understood that the procedure can be readily adapted by persons skilled in the art to detectors having a different number of pixels.
  • the first step in the procedure is to select the center 1024 pixels out of the 2048 pixels of raw data in order to reduce the calculation time while still providing sufficient resolution.
  • each of the data values for the 1024 center pixels is multiplied by a complex modulation of the form: exp(-i ⁇ n ⁇ x ⁇ 2 ⁇ /2048) where i is the square root of -1, n is the number of the pixel, and x is the desired modulation value selected so that the shifted spatial frequency of the position peak is close to but greater than zero.
  • a preferred value for x for a 16° detector is 192 which will shift 12 cycles/degree to zero.
  • the next step in the procedure is to filter the modulated data values with a 26 tap low pass FIR filter.
  • the filter is applied to remove any aliases generated in decimation step 203.
  • the filter has a notch at the frequency of the DC component as shifted by modulation step 201.
  • Preferred coefficients for the filter are set forth in Table 1. With these coefficients, the average attenuation of the filter is -30 dB.
  • the next step is to decimate the 1024 pixels by 16 to 1. This step is done to reduce the calculation time of the complex fast Fourier transform (FFT) while still retaining sufficient resolution.
  • FFT complex fast Fourier transform
  • the pseudopixels are then windowed in step 204 to reduce signal leakage and ringing, and thus allow the spatial frequency of the position peak to be determined with sufficient resolution.
  • the pseudopixels are preferably windowed with a Blackman-Harris window of the form: 0.35875 - 0.48829 ⁇ cos(2 ⁇ n/63) + 0.14128 ⁇ cos(4 ⁇ n/63) - 0.01168 ⁇ cos (6 ⁇ n/63) where n is the pseudopixel index ranging from 0 to 63.
  • the next step is to perform a 64 point complex FFT to transform the pseudopixel values into spatial frequency values.
  • the complex FFT can be performed using the Cooley, Lewis, and Welch technique as described in their paper entitled “The Fast Fourier Transform and its Applications,” IBM Research Paper RC 1743, February 9, 1967. See also Rabiner and Gold, Theory and Application of Digital Signal Processing, Prentice-Hall, New York, 1975, page 367; and Cooley et al., IEEE Transactions in Education , March 1969, pages 27-34. Other techniques can be used if desired.
  • the frequency coefficients generated by the complex FFT are left in magnitude squared form.
  • a complex FFT is used because it produces 64 frequency coefficients out of 64 pseudopixels. Also, the heterodyne peaks will wrap around from 0 to 63 instead of reflecting off of zero frequency. The value of such wrapping around can be seen as follows.
  • the position component Because of the presence of the diameter component, the position component has two heterodynes which for a 125 micron fiber are spaced on either side of the position component by about 3.1 cycles/degree (see above). If the position component is shifted from about 13.7 cycles/degree to about 1.7 cycles/degree after steps 202 through 204 have been performed, then the heterodynes will fall at about -1.4 cycles/degree and about 4.8 cycles/degree.
  • the lower heterodyne is wrapped around to about 6.6 cycles/degree. If a FFT were used, the lower heterodyne would be reflected to about 1.4 cycles/degree and would thus interfere with the position peak at about 1.7 cycles/degree.
  • the final step in the procedure is the determination of the value of ⁇ D .
  • the position peak is the largest peak. Accordingly, the position peak location is determined by first finding the largest frequency space peak. A parabolic fit is then performed on the magnitude of this largest peak and the magnitudes of the peaks on either side of the largest peak. The location of the position peak is then the spatial frequency at which this parabolic curve has its maximum value.
  • one of the heterodynes can be larger than the position peak for certain fiber positions.
  • the position peak is therefore found by limiting the region of search for the largest peak to exclude the heterodynes, e.g., for the numerical values discussed above, the search for the largest peak would be limited to below about 2.3 cycles/degree.
  • Figures 10 and 11 show the results of applying the procedure of Figure 9 to the problem of determining the position of an optical waveguide fiber.
  • the data shown in these figures was obtained using the apparatus of Figure 4.
  • the Ronchi ruling employed had a ⁇ M value of 12.3 cycles/mm and a duty cycle of 15%. No drift was observed for the system over an extended period of use.
  • the vertical axis in Figure 10 sets forth the ⁇ D values at detector 31 determined using the procedure of Figure 9 and the horizontal axis sets forth the actual position of the fiber as measured using a test fixture which allowed a segment of fiber to be positioned to within a few microns.
  • the vertical axis in Figure 11 shows the differences (residuals) between the actual positions and the ⁇ D positions and the horizontal axis again shows the actual positions. (Note that the system will normally be calibrated using a curve like that of Figure 10.)
  • the foregoing procedures for monitoring the position of a fiber are preferably combined with the fiber diameter measurement, defect detection, and hermetic coating monitoring procedures of the above-referenced EPO Patent Publication No. 608,538 and U.S. Patents Nos. 5,185,636 and 5,309,221.
  • the procedures are also preferably combined with the techniques for measuring the diameters of non-circular fibers set forth in U.S. Patent No. 5,283,628.
  • two detectors are preferably used in these techniques, thus giving two measurements for the position of the fiber when the methods and apparatus of the present invention are employed with each detector.
  • the exact position of the fiber in the plane defined by laser beam 25 can be readily determined by using the known positions of the Ronchi rulings which would be placed before lens systems 26,27 in such an overall control system and/or by calibration.
  • FIG. 12 shows a system for determining the distance "D" from a Ronchi ruling 150 to a point 141 on a scattering, e.g., diffusely reflecting, surface 113.
  • the system includes a lens system 127 and a detector 131 located in the back focal plane of the lens system. As discussed above, the lens system is optional and may be omitted if desired.
  • point 141 on surface 113 is shown located in the front focal plane of the lens system for ease in drawing light rays 143 through 146. The point on the surface whose distance is to be determined of course does not need to be at this position.
  • Light source 123 produces light beam 125 which passes through aperture 147 in detector 131, lens system 127, and transparent slit 148 of Ronchi ruling 150.
  • the light source may be located above or below detector 131, in which case the detector does not need to include an aperture.
  • the light source need not produce a coherent monochromatic beam of light, although such a beam can be used if desired, e.g., a laser can be used as the light source. Rather, a light source of any type can be used provided it produces a small spot of light at surface 113 so that the shadows of Ronchi ruling 150 have a sufficient contrast at detector 131.
  • the system of Figure 12 operates in accordance with the principles set forth above and thus the distance "D" is given by equation (4).
  • the system has a number of advantages in comparison to existing systems for determining the distance to a surface with high precision.
  • the system has a number of advantages over laser triangulation systems which have been used in the past to make such measurements.
  • Laser triangularization systems can be designed to provide features (1) through (3), but such systems do not have these features intrinsically and thus to provide the features, the cost and complexity of the system must in general be increased.
  • Feature (4) cannot be incorporated in laser triangularization systems since such systems require a substantial included angle between the beam which strikes the surface and the detector, e.g., an angle of at least about 15°. Indeed, the sensitivity of a laser triangularization system increases as the included angle increases.
  • the present invention is free of this deficit since the included angle between the beam and the detector can be as small as ⁇ 4° or even less.
  • the process of the invention as described above is preferably practiced on a digital computer system configured by suitable programming to perform the various computation and identification steps.
  • the programming can be done in various programming languages known in the art.
  • a preferred programming language is the C language which is particularly well-suited to performing scientific calculations.
  • Other languages which can be used include FORTRAN, BASIC, PASCAL, C ++ , and the like.
  • the computer system can comprise a general purpose scientific computer and its associated peripherals, such as the computers and peripherals currently being manufactured by Digital Equipment Corporation, IBM, Hewlett-Packard, or the like.
  • a dedicated system can be used in the practice of the invention, such as a system using multiple digital signal processing chips.
  • the processing portion of the computer system should have the following characteristics: a processing rate of 50 million floating point operations per second, a word length of 32 bits floating point, at least four megabytes of memory, and at least 40 megabytes of disk storage.
  • the system should include means for inputting data from the photodetector array and means for outputting the results of the position determination both in electronic form for use in process control and in visual form for observation by system operators, maintenance personnel, and the like.
  • the output can also be stored on a disk drive, tape drive, or the like for further analysis and/or subsequent display.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Length Measuring Devices By Optical Means (AREA)
  • Measurement Of Optical Distance (AREA)
  • Manufacture, Treatment Of Glass Fibers (AREA)
  • Optical Radar Systems And Details Thereof (AREA)

Claims (15)

  1. Un procédé pour surveiller l'emplacement d'un filament (13) comprenant les opérations consistant :
    (a) à diriger un faisceau de rayonnement sur le filament de sorte qu'une portion du filament comprenne une source lumineuse diffusante ;
    (b) à moduler spatialement de la lumière provenant de ladite source lumineuse diffusante, ladite modulation spatiale ayant une fréquence spatiale wM ;
    (c) à détecter ladite lumière modulée spatialement ; et
    (d) à déterminer une fréquence spatiale WD pour la lumière détectée modulée spatialement, ladite fréquence spatiale WD étant fonction de WM et de la distance séparant le filament de l'endroit où la lumière est modulée spatialement à la fréquence WM.
  2. Le procédé de la revendication 1, dans lequel l'opération (d) est effectuée :
    en générant un spectre de fréquences spatiales pour ladite lumière détectée modulée spatialement; et
    en identifiant une composante dudit spectre de fréquences spatiales ayant ladite fréquence spatiale wD qui est représentative de ladite distance.
  3. Le procédé de la revendication 1 ou 2, dans lequel on utilise un réseau de Ronchi (50) pour effectuer ladite opération (b).
  4. Le procédé de l'une quelconque des revendications précédentes, dans lequel entre les opérations (b) et (c), on transforme ladite lumière modulée spatialement au moyen d'un système à lentille (27) de sorte que ladite distance soit une fonction linéaire de WD.
  5. Le procédé de la revendication 2, ou de l'une des revendications 3 et 4 en rattachement à la revendication 2, dans lequel le filament (13) est transparent et le faisceau de rayonnement produit une figure d'interférence qui est détecté à l'opération (c).
  6. Le procédé de la revendication 5, dans lequel le spectre de fréquences spatiales comprend une composante de diamètre extérieur qui est utilisée pour surveiller le diamètre du filament.
  7. Le procédé de la revendication 6, dans lequel la composante de diamètre extérieur a une fréquence spatiale wOD et dans lequel WM est choisi en sorte que wOD soit sensiblement inférieur à (i) WD et (ii) à WD -wOD pour les emplacements et diamètres attendus du filament.
  8. Le procédé de la revendication 6 ou 7, dans lequel le spectre de fréquences spatiales est utilisé pour surveiller l'épaisseur d'un revêtement hermétique sur le filament (13).
  9. Le procédé de l'une quelconque des revendications précédentes, dans lequel les opérations (b) à (d) sont exécutées en chacun de deux emplacements spatialement distants.
  10. Le procédé de la revendication 9, dans lequel le faisceau de rayonnement définit un axe (51), et les deux emplacements spatialement distants sont tous deux décalés angulairement par rapport à l'axe.
  11. Un procédé pour asservir l'emplacement d'un filament, comprenant la surveillance de l'emplacement du filament par le procédé de l'une quelconque des revendications précédentes, et comprenant l'opération supplémentaire de génération d'un signal d'asservissement pour l'emplacement du filament à partir de la valeur de WD.
  12. Appareil pour mesurer la distance à une surface, en combinaison avec un objet ayant ladite surface, l'appareil comprenant :
    un moyen de détection (29, 31; 131) propre à détecter de la lumière en une pluralité d'emplacements répartis dans l'espace ;
    un moyen d'illumination (23, 123) propre à diriger un faisceau de lumière sur la surface de sorte qu'au moins une portion du faisceau de lumière soit diffusé par la surface sur le moyen de détection ;
    un moyen de modulation spatiale (50, 150) entre la surface et le moyen de détection pour moduler spatialement la lumière diffusée, ladite modulation spatiale de la lumière diffusée ayant une fréquence spatiale wM ;
    un moyen (201-206) propre à déterminer une fréquence spatiale WD de la lumière diffractée et modulée spatialement sur le moyen de détection, la distance comprise entre le moyen de modulation spatiale et la surface étant fonction de wD et wM.
  13. La combinaison de la revendication 12, dans laquelle le moyen de modulation spatiale (50, 150) est un réseau de Ronchi.
  14. La combinaison de la revendication 12 ou 13, comprenant en outre un système à lentille (26, 27; 127) entre le moyen de modulation spatiale (50, 150) et le moyen de détection (29, 31; 131), ledit système à lentille ayant une puissance positive et le moyen de détection étant dans le plan focal arrière du système à lentille, d'où s'ensuit que la distance D comprise entre le moyen de modulation spatiale et la surface est une fonction linéaire de WD.
  15. La combinaison de l'une quelconque des revendications 12 à 14, dans laquelle ledit objet est un filament.
EP95119165A 1994-12-30 1995-12-06 Méthode pour déterminer la position d'une fibre optique Expired - Lifetime EP0720001B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US08/368,311 US5519487A (en) 1994-12-30 1994-12-30 Method for monitoring the position of a fiber
US368311 1994-12-30

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EP0720001A2 EP0720001A2 (fr) 1996-07-03
EP0720001A3 EP0720001A3 (fr) 1997-04-23
EP0720001B1 true EP0720001B1 (fr) 2002-04-10

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EP (1) EP0720001B1 (fr)
JP (1) JP3677639B2 (fr)
KR (1) KR960024248A (fr)
AU (1) AU686910B2 (fr)
BR (1) BR9506096A (fr)
CA (1) CA2163161A1 (fr)
DE (1) DE69526321T2 (fr)
DK (1) DK0720001T3 (fr)
RU (1) RU2152589C1 (fr)
TW (1) TW302433B (fr)
UA (1) UA32584C2 (fr)

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JP3677639B2 (ja) 2005-08-03
AU686910B2 (en) 1998-02-12
RU2152589C1 (ru) 2000-07-10
AU4054295A (en) 1996-07-11
EP0720001A2 (fr) 1996-07-03
DK0720001T3 (da) 2002-07-29
BR9506096A (pt) 1997-12-23
UA32584C2 (uk) 2001-02-15
KR960024248A (ko) 1996-07-20
CA2163161A1 (fr) 1996-07-01
US5519487A (en) 1996-05-21
EP0720001A3 (fr) 1997-04-23
JPH08247711A (ja) 1996-09-27
TW302433B (fr) 1997-04-11
DE69526321T2 (de) 2002-09-05
DE69526321D1 (de) 2002-05-16

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